It was 2008 and the traveling rock/punk festival was winding down for the summer. Perry, who had just released debut pop album One of the Boys that June, was riding high on a little breakthrough called I Kissed a Girl (the first of her now nine No. 1 hits on the Billboard Hot 100 singles chart).

But in a "yearbook" given to artists at the end of the trek, "someone voted me 'laziest' because they thought I was just sleeping in my bus because they never saw me," Perry says. "The actual reality is, I was up at 7 a.m. doing radio promo and then going to dinner with program directors after my shows. I was always hustling."

Still, she laughs, "can you imagine being voted 'laziest?' Cut to eight years later, I'm doing a yearlong tour and 141 shows and counting."

Perry is just one of many eventual superstars to cut their teeth on the annual Vans Warped Tour, which brings dozens of rising to mid-level acts on a coast-to-coast jaunt that attracts an average of 500,000 concertgoers each summer. Now in its 20th year, the genre-spanning festivals have become breeding grounds for bands such as Fall Out Boy, Paramore and Blink-182, as well as hip-hop and dance acts such as The Black Eyed Peas, Eminem, Skrillex and M.I.A. This season's 41-city run kicks off Friday in Pomona, Calif., and features artists as varied as Motion City Soundtrack, Bebe Rexha and Riff Raff.

Warped was founded in 1995 by Kevin Lyman, a live promoter who managed Lollapalooza tours for three years prior, but wanted to bring the spirit of the California skateboarding scene to a festival setting. Recruiting artists he knew from L.A. clubs such as No Doubt (with Gwen Stefani) and Sublime for the inaugural Warped lineup, Lyman describes that first summer as a bit of a "disaster" — with promoters unsure of how to advertise the event or who it was for.

Now drawing a crowd that is 92% 15 to 25-year-olds (56% of whom are female), Warped's one-day stops aim to wrap by 9 p.m. each day, which gives parents peace of mind that kids "were going somewhere and coming home that night," Lyman says. And with the vast majority of fans arriving when gates open late morning, "the kids are there to see all the artists. I think that's been the key to breaking acts on this tour."

For Pete Wentz, Warped was "a lot like summer camp" when his band Fall Out Boy played in 2004 and 2005, just as the punk-rockers were set to break out with album From Under the Cork Tree. Touring with friends like My Chemical Romance and Gym Class Heroes, "it was super democratic," he says. "Some days we might play at 11 a.m., sometimes we might play at 8 p.m." With a varying schedule compiled by Lyman every day, "there was no way to rig the system and I thought that was pretty cool. No matter who you were, everyone was pretty equal on the tour."

With artists playing half-hour sets on as many as 10 stages at once, you really had to "try to win (people) or earn them, which was cool. I feel like our band is a better band because of that," Wentz says. It's a sentiment that Perry echoes, given that she was a pop artist on a heavy-metal and punk-dominated lineup.

"There's an intense level of confidence that sweeps over me and I can really command a stage, and back then, I could do it, too. I just had to. I had to fake it until I made it," Perry says. Heavily influenced by Alanis Morissette and Garbarge at the time, it helped that songs off One of the Boys were more guitar-based, so she played with a full band and kept the choreography to a minimum. "A lot of times you'd just find me hanging over the crowd," or "stage-diving and throwing myself into the pit," she says. "I was very involved in that kind of lifestyle."

Although her sound has evolved and she no longer drives around in a Myspace-sponsored bus with her face plastered across the side, "I still have a bit of that California punk-rock attitude always with me," Perry says. "I'm happy that my first tour was Warped Tour. I really got my bearings there."